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Nutrient management for garden crops

Stock image provided by Tom Jacobsen
Plants require 17 different nutrients to complete their life cycle. Each nutrient is needed in different amounts, and each plant needs different amounts. In agricultural environments where one crop is being managed , nutrient management is straightforward. However, in gardens where several different crops are being managed, nutrient management is more complex and a plan for managing nutrients for maximum crop yields becomes a higher priority.
Essential nutrients
Essential plant nutrients can be broken down into two groups, those that are needed in large amounts are macronutrients, and those needed in small amounts are micronutrients. Some nutrients do not need to be applied via fertilizer, hydrogen (H), oxygen (O), and carbon (C) are supplied to plants through water and Carbon dioxide. Nitrogen (N), phosphorus (P), and potassium (K) are needed in the largest amounts. These are the primary nutrients listed on all fertilizers as the guaranteed analysis N-P-K. They are listed as a percentage of the total fertilizer, so a 10-10-10 guaranteed analysis indicates 10 percent N, 10 percent P, and 10 percent K. Additional macronutrients include sulfur (S), calcium (Ca), and Magnesium (Mg). These are referred to as secondary nutrients and are needed in smaller amounts than N, P, and K.
Micronutrients include chlorine (Cl), iron (Fe), boron (B), manganese (Mn), zinc (Z), copper (Cu), molybdenum (Mo), and nickel (Ni). Fertilizer labels will indicate the amount of each nutrient in order from the highest to lowest concentration.
Each nutrient has a specific role in plant growth and development. In addition, when plants are deficient in any nutrient, they will display symptoms of those deficiencies.
Factors affecting nutrient availability
Several factors influence what nutrients are available to the crop being produced. First, what is already in the soil should influence nutrient management. A soil test should be taken each year to inform your decisions. Your local extension educator can help you understand how to properly collect a soil sample and send it in to a laboratory for testing. They can also help you to interpret the results of the test.
One of the things you will learn from your soil test is what pH your soil is. Soil pH is a measurement of the hydrogen ions in the soil. You might recall from your high school science classes that the pH scale goes from 0-14, that 7 is neutral, and anything below 7 is acidic and anything above 7 is basic or alkaline. Each nutrient becomes available to a plant with a different pH level. For example, phosphorus (P) becomes available to a plant between a pH of 6.0 and 7.0. At lower levels, phosphate tends to bind with aluminum or iron compounds in the soil, making less available for plant uptake. At higher levels, phosphate tends to precipitate with calcium.

Roques, Susie & Kendall, Sarah & Smith, K.A. & Newell Price, Paul & Berry, P. (2013). Review of the non-NPKS nutrient requirements of UK cereals and oilseed rape. | Tom Jacobsen
Another factor influencing availability of nutrients is soil texture. The soil solution is the liquid in the soil Plant nutrients (solids and gases) dissolved in the soil solution can move into the plant as the water is taken up by the roots. Positively charged cations (such as Ca+, Mg2+, K+, and NH4+) are held to negatively charged anions in the soil. Clay particles have many more anionic exchange sites than silt or sand. The Cation Exchange Capacity (CEC) is the measure of the number of cations that can be held by the soil and released into the soil solution. Soils with higher CEC can hold onto more nutrients, so even if the nutrients are in the soil, they may not be available to plants.
Organic matter in the soil is a very good thing, but that organic matter is in various stages of decomposition. Humus is organic material resistant to further decomposition and does not supply many nutrients. It can increase the CEC of the soil.
Soil structure can impact nutrient availability as well. In compacted soils, small spaces between soil particles prevent the soil solution from moving throughout the soil profile, resulting in runoff. Large spaces also impact nutrient availability as nutrients like N will leach through the soil easily.
How to apply fertilizers on gardens
Fertilizers should be applied based on the average nutrient requirements of all the crops being raised. You can also rotate your crops within your garden to take advantage of plants that naturally add nutrients to the soil. Legumes like peas and beans will add N to the soil, where other plants use N in high amounts.
Application methods also differ. Broadcasting is where you apply even amounts of fertilizer to the surface of the garden. This is usually done before tilling and the use of a rototiller incorporates the nutrients into the soil. A second application method is banding or sidedressing. This refers to placing nutrients above, below, or on the side of the seed during planting. This helps by putting the fertilizer where the plants can use it quickly and efficiently. It also requires less fertilizer than broadcasting. Disadvantages of this include increased leaching of N and S. It also requires machinery or equipment that many gardeners may not have access to.
Many of our garden plants should have fertilizer applied prior to planting, then again later in the season. Be careful to only apply what is needed, the idea that if some is good, more is better does not work with fertilizer. Later in the season you can sidedress many of the plants that need extra fertilizer, like corn. Only apply correct amounts, and in some cases, less is more. Tomatoes, for example, are designed to grow in places with longer growing seasons than we have in Idaho. If you apply extra nitrogen fertilizer, it will lengthen the time it takes to fruit beca
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Source: eastidahonews.com

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